Control mechanism for electrically operated lifters



| G. KAPLAN 3,097,875

2 Sheets-Sheet l m mm 8 me. u 6 0 I N5 \Q m I Pi f I w Z 2 6 LA l "TY. \M. E: F )L Q m O w m 3 m W 1 w WM" 0 3 July 16, 1963 CONTROL MECHANISM FOR ELECTRICAL-LY OPERATED LIFTERS Original Filed Dec. 23, 1957 M ATTY.

L- G. KAPLAN July 16, 1963 CONTROL MECHANISM FOR ELECTRICALLY OPERATED LIFTERS 2 Sheets-Sheet 2 Original Filed Dec. 23, 1957 INVENTOR. Low 5 G. KAPLAN BY United States Patent 3,097,875 CONTROL MECHANISM FOR ELECTRICALLY OPERATED LIFTERS Louis G. Kaplan, Evanston, IlL, assignor to Cullen- Friestedt -Company, Chicago, Ill., a corporation of Illinois Original application Dec. 23, 1957, Ser. No. 704,385, n'ow Patent No. 2,959,411, dated Nov. 8, 1960. Divided and this application Mar. 2, 1959, Set. No. 796,506

1 Claim. (Cl. 294-67) The improved control mechanism comprising the present invention has been designed for use primarily in connection with lifter mechanisms of the type shown and described in my copending application Serial No. 704,385, filed December 23, 1957, now US. Patent No. 2,959,411, granted on November 8, 1960, and entitled Shock Absorbing Linkage Mechanism, of which application the present one is a division. The invention is however capable of other uses and the same may, if desired, with suitable modification where required, be employed for other purposes in connection with electrically powered mechanism, particularly in instances where reversible electric motors are concerned which require a greater torque when the motor is running in one direction than when it is running in the opposite direction. The invention has, for illustrative purposes, been illustrated and described herein as being operatively associated with a litter mechanism of the type shown in my copending application cited above but it will be understood that various other uses are contemplated and that irrespective of the particular use to which the invention may be put, the essential features of the invention remain substantially the same.

Lifter mechanisms of the type shown and described in the above-mentioned copending application, as well as a wide variety of other lifter mechanisms having opposed jaws capable of relative outward and upward swinging motion for jaw opening and jaw closing purposes, frequently encounter a condition whereinthe actuating motor for the jaw mechanism runs at excessive speeds during closing movements of the jaws. The structures involved, being relatively massive, the weight of the jaws is appreciable and, under no-load conditions when the jaws are swinging downwardly and inwardly toward each other to efiect their closing movements, the moment of torque which is applied to the rock-shaft or other jaw actuating member, under the influence of gravitational force, is sufficiently great that this torque will be applied through the train of driving mechanism leading to the motor shaft, thus causing excessive motor speed. This condition is especially prevalent in connection with a litter mechanism which utilizes a heavy angle bar type gripping member at the outer ends of the jaw arms where the gravitational force exerted thereby through the arms to the rock-shaft or other actuating member is comparatively great by virtue of the distance of the gripping jaws from the pivotal points of the swinging jaw arms and the relatively large moment of gravitational force applied to the arms by virtue of such distances. Where series wound direct current motors are concerned, a light load, a zero load, or a negative load such as may be applied to the motor under the conditions outlined above may allow the motor to run away and destroy itself, while at the same time there is likelihood that the article to be lifted will become damaged due to the relatively high velocity of the jaws at the moment of engagement. The present invention is designed .to overcome the above-noted limitation that is attendant upon the use of litter mechanisms of the type described above and, toward this end, it contemplates the provision of a novel control means whereby excesice sive speed of the actuating motor for the lifter may be avoided during closing movements of the lifter jaws.

According to the present invention, and in order to accomplish the above aims, it is contemplated that automatic means be provided for introducing a resistance into the motor circuit when the motor controls are set for operation of the motor in one direction only. When such controls are set for operation of the motor in the opposite direction, such automatic means is effective to remove the resistance from the motor circuit and allow the motor to operate at full line voltage. Still further, according to the invention, it is proposed that the resistance element or resistor be mounted directly on or adjacent the motor, or at least that it be mounted on and become a permanent part of the lifter assembly. By such an arrangement, a resistor of the proper ohmic value for any given lifter installation may be selected so that it may become individual to that particular lifter installation and to no other so that intricate control panel wiring is not necessary where a large variety of litters or other motor-operated instrumentalities are to be operated, for example, from any given overhead crane assembly. The circuit of the present invention contemplates the use of a relay circuit including a high impedance magnet coil which is arranged in the circuit in such a manner that certain rectifier and limit switch mechanism employed in connection with the invention will be subject to extremely low current flow, thus making possible the use of small commercial type limit switches and inexpensive radio type rectifiers.

Yet another advantage accrues from the provision of the present invention. The usual procedure for reducing motor torque or for stopping the operation of a motor when a litter mechanism has completed its stroke, or when it has met with an obstruction, is to provide a limit switch, or a pair of such switches, on the lifter mechanism, such switch or switches being electrically connected to the motor control panel. Since the control panel is frequently mounted at a remote point, for example, in the cab of the overhead crane, various power leads including self-winding pulleys and the like, are necessary and greatly increase the cost of the equipment. According to the present invention, by mounting ing all of the electrical equipment, including the resistor, all of the electrical equipment, including the resistor, limit switch or switches, rectifier, relay devices etc., on the lifter, with only the reversing switch being retained on the control panel, a very material reduction in equipment is attained.

The provision of a control mechanism which will accomplish the above-noted functions in the novel manner indicated being among the principal objects of the invention, other objects and advantages of the invention, not at this time enumerated, will become more readily apparent as the following description ensues.

In the accompanying two sheets of drawings forming a part of this specification, one exemplary form of the invention has been shown.

In these drawings:

FIG. 1 is a fragmentary vertical sectional view taken through a litter assembly in the vicinity of the power actuated gear driving mechanism therefor and showing a limit switch which forms a part of the control system of the present invention operatively applied thereto; and

FIG. 2 is a circuit diagram for the electric motor associated with the lifter and illustrating the improved control mechanism of the present invention operatively associated therewith.

Referring now to the drawings in detail and in particular to FIG. 1, for exemplary purposes the control mechanism of the present invention is shown as being operatively applied to a lifter of the general type shown and described in my abovementioned copending application. Only such portions of the lifter mechanism as are necessary to a general understanding of the conditions which may arise and which may create a condition of mechanical motor overload have been illustrated herein and for a detailed description of the entire mechanism and its mode of operation, reference may be had to such copending application.

The lifter involves in its general organization an elongated supporting element 1t), a pair of jaw assemblies 11 and 12, a reversible electric motor M, and a power train 13 extending between the motor and jaws for conjointly shifting the latter toward and away from each other in response to the operation of the motor. At suitable spaced points along the supporting element there are provided a series of spaced attachment or pivot lugs 14, only one such lug being disclosed herein. Each lug 14 has pivotally connected thereto on opposite sides thereof one of the pairs of jaw assemblies 11 and 12. The two jaw assemblies are identical in construction and each is in the form of a composite assembly including an upper or proximate jaw section 16 and a lower or distal jaw section 18 hingedly connected as at 20 to the upper section. The upper jaw section 16 is comprised of a pair of laterally spaced flat metal bars 22 and 24, the upper ends of which straddle the pivot lugs 14, while the lower section 18 is in the form of a single flat metal bar, the upper region of which extends between the bars 22 and 24. Toothed sector means 26 on the lower section =18 is adapted to cooperate with a locking bar 28 in such a manner that the angular position of the lower jaw section relative to the upper jaw section may be adjusted. The lower ends of the lower jaw sections 18 carry opposed angle bar gripping members 30.

The electric motor M by means of which the jaws 11 and 12 are actuated is preferably of the reversible direct current type. The motor includes a casing 32 which is secured as at 34 by welding to the supporting member 10. The motor M has operatively associated therewith a gear reduction mechanism 36 having an output shaft 38 carrying a pinion 40 constituting one element of the previously mentioned power train 13. The power train 13 which extends between the output shaft 38 of the gear reduction device 36 and the jaws 11 and 12 is comprised of a set of gearing including the pinion 40 and a linkage mechanism 42. The gearing, in addition to the pinion 40, comprises a gear segment 44 which meshes with the pinion 4t and which is keyed to a rock-shaft 46. Also keyed to the rock shaft 46 are a pair of bifurcated crank arms 50 and 52 which extend radially outwardly from the rock shaft 46 in opposite directions. The distal end of the crank arm 50 is pivotally connected as at 53 to one end of a thrust link 54, the other end of the link being pivotally connected as at 56 to a medial region of the upper jaw section 16. The distal end of the crank arm 52 is pivotally connected as at 58 to one end of a spring biased lost motion link assembly designated in its entirety at 60", the other end of the link assembly being pivoted as at 61 to a medial region of the upper jaw section 16 of the jaw 11.

The details of the link assembly 60 constitutes the subject matter of my above-mentioned patent and no claim is made herein to any novelty associated therewith. Since the link assembly involves in its general organization a certain limit switch mechanism, designated in its entirety at 62, which is pertinent to the control mechanism of the present invention, only this switch mechanism and such portions of the link assembly as serve to actuate the same will be described herein and reference may be had to such patent for a more detailed description of the link assembly.

It is deemed suflicient for purposes of disclosure herein to state that the link assembly 60 includes an inner link member 64 and an outer encompassing link member 66. The two link members bear a telescopic relation to each other with the outer link member 66 being connected to the pivot point 61 and with the inner link member 64 being connected to the pivot point 58. The limit switch 62 is fixedly mounted on the outer link member 66 and is designed for engagement and actuation under the control of a collar 68 carried by the inner link member 64. Toward this end, the limit switch 62 is provided with an actuating finger 76 (see also FIG. 2) which is positioned in the path of movement of the collar 68 so that when the latter moves to the left relative to the link member 64 as seen in FIG. 1, the collar will engage the finger 70 and actuate the limit switch 62. Such movement of the collar into engagement with the actuating finger 71) takes place when compressional forces are applied to the opposite ends of the link assembly 60' after an external shock is encountered by the lifter jaws 11 and 12, as, for example, when these jaws during outward swinging movement thereof under the motivating influence of the motor M encounter an adjacent massive object, or when the jaws 11 and 12 become wedged between two opposed immobile adjacent objects. The limit switch 62 is provided with a pair of normally open contacts 0 (FIG. 2) adapted to become closed under the influence of the actuating finger 70. The circuit connections for the limit switch will be described presently.

As previously stated, the reversible electric motor M is of the series wound, direct current type wherein reversal of the direction of current flow through the motor armature will effect reversal of the direction of rotation of the motor shaft, this shaft being designated at 74 in FIG. 2. Reversal of the direction of rotation of the motor shaft 74 will, of course, cause reversal of the output shaft 38 of the gear reduction device 36 and of the entire power train mechanism 13. Such selective reversal of the current flow through the armature circuit will control the direction of movement of the lifter jaws 11 and 12.

In order to prevent excessive motor speeds during inward swinging movement of the jaws '11 and .12 under the influence of gravitational forces acting on the jaws, means are provided whereby full line current will be applied to the armature circuit with the current flowing through the circuit in a direction to cause clockwise rotation of the rock-shaft as viewed in FIG. 1 and consequent opening movement of the jaws 11 and :12. The motor M will thus be driven under full power. However, when the direction of current flow through the armature circuit is reversed so that the power train 13 is actuated to cause counterclockwise rotation of the rock-shaft 46 to effect closing movement of the jaws '11 and 12, automatically operable means are provided for introducing a resistance element into the armature circuit so that the motor will be driven under reduced power. The circuit diagram of FIG. 2 illustrates schematically the manner in which such a resistance is automatically introduced into the armature circuit of the motor and it also illustrates the manner in which the limit switch 62 is capable of reducing the flow of current through the armature circuit when the lifter jaws L11 and 12 encounter opposition as previously outlined.

Referring now in detail to FIG. 2, full line current may be applied to the armature circuit of the motor M from the positive side of the line, through lead 17, field winding F of the motor M, lead 19, a reversing switch 80, leads 21, 23, armature A of the motor M, leads 25, 27, a pair of normally closed contacts c associated with a relay magnet M leads 31, 33, 35 and reversing switch to the negative side of the line. Current flowing through the armature of the motor M in this direction will move the rock-shaft 46 in a clockwise direction as seen in FIG. 1 so as to cause opening movements of the jaws :11 and 12. Upon operation of the reversing switch 80 in such a manner as to reverse the direction of current flow through the armature of the motor M, a circuit will exist from the positive side of the line, through lead :17, field winding F of the motor M, lead 19', the reversing switch 80, leads 35, 37, relay magnet M leads 39, 41, a unidirectional device SR which may be in the form of a selenium rectifier, leads 4'7, 49, 21, and reversing switch 80 to the negative side of the line. Energization of the relay magnet M will cause opening of the contacts thus establishing a circuit extending from the positive side of the line, through the reversing switch 80, leads 35, 33, 51, resistance R, leads S3, 25, armature of the motor M, leads 23, 21 and reversing switch 80 to the negative side of the line. The ohmic value of the resistor R may be selected according to engineering requirements to produce a desired voltage drop across the resistor and reduce the current flow through the motor armature to such an extent that over-speeding of the motor M under the influence of gravitational forces acting upon the jaws 311 and 12 during closing movements thereof will be avoided.

The contacts c of the limit switch 62 are disposed in shunt relationship with the unidirectional device SR so that when the actuating finger 70 is engaged by the collar 68, and the contacts 0 become closed, the unidirectional device SR will be bypassed and a shunt circuit passing through lead 43, contacts 0 leads 45, 39, and magnet M will be completed, thus opening the contacts c and re storing the circuit through the resistor R and motor armature so as to reduce the power output of the motor M. Such a condition will obtain, for example, when compressional forces are applied to the ends of the link assembly 60 due to the lifter jaws becoming wedged between two adjacent objects during opening of the jaws under full motor power in the manner previously indicated.

According to the present invention, the electrical components including the motor M, magnet M contacts 0 and limit switch 62 including the contacts are operatively carried by the lifter assembly while the reversing switch '80 may be disposed at a remote location, for example in a control panel CP disposed in the cab of an overhead crane. The lifter-contained components have been enclosed within a dotted line rectangle in FIG. 2 labelled LM and representing the lifter mechanism, while the reversing switch 80 has been enclosed by a dotted line rectangle labelled CP and representing the control panel which, as previously stated, may be positioned in the cab of an overhead crane.

The disposition of the limit switch 62 and motor M on the lifter assembly has previously been described. The other electrical components, namely the resistor R, relay magnet M and the contacts 0 may conveniently be disposed within a shield housing 90 conveniently positioned on the lifter framework, as for example on one of the pivot lugs 14 associated with the supporting element 10. The resistor R thus becomes a permanent part of the lifter assembly where it is available for introduction into and removal from the motor circuit. Since the resistor R is individually identified with the motor M, no circuit changes or resistor substitutions need be made when the particular lifter assembly becomes associated with the control panel of an overhead crane.

While one specific and preferred form of the motor control system by means of which the principles of the invention may be carried out has been illustrated and described herein, it will be understood that this form of the system does not by any means indicate the only form 6 contemplated. The form illustrated herein is only one which has been developed for commercial application of the system.

The invention is not to be limited to the details described, since these may be modified within the scope of the appended claim without departing from the spirit of the invention.

Having thus described the invention what I claim as new and desire to secure by Letters Patent is:

In a lifter construction of the character described, a lifter framework, a pair of cooperating lifter jaws pivoted to said framework and each swingable about a horizontal axis from an elevated open jaw position to a lowered closed jaw position wherein they may engage an article to be lifted therebetween, a crank arm interposed between said lifter jaws for actuating the same, a lost motion connection between said crank arm and one of said lifter jaws, a limit switch operable under the control of said lost motion connection, said limit switch including a pair of normally open contacts adapted to become closed when the limit switch is operated by said lost motion connection, a reversible series wound direct current motor carried by the tramework :for moving said jaws between their open and their closed positions, a power train operatively connecting said motor and jaws, an armature circuit for said motor, a source of direct current for energizing said circuit, -a reversing switch remote from the lifter and operable to selectively energize said armature circuit with current of opposite polarity from said source, a pair of normally closed relay-actuated contacts in said armature circuit, a relay magnet operable upon energization thereof to open said normally closed contacts, a circuit for the magnet operatively connected to said source through said reversing switch, a unidirectional device in said magnet circuit, and a current limiting resistance disposed in said armature circuit and arranged in shunt relation across the pair of normally closed contacts, said unidirectional device establishing current fiow in the magnet circuit when the polarity current applied to the armature is of such polarity as to cause said motor to move said jaws toward their closed positions through the medium of said power train, said limit switch being disposed in said magnet circuit in shunt relation to the unidirectional device, said normally closed relay-actuated contacts, relay magnet, unidirectional device, and current-limiting resistance being mounted on and bodily movable with the lifter firam'ework.

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